Planar antenna on electrically—insulating sheet

ABSTRACT

A generally planar TV antenna having preferably at least two pairs of spaced-apart electrically conductive lands ( 3, 5; 7, 9 ) disposed on a sheet of electrically-insulating material ( 1 ) and method of manufacturing such antenna by providing the lands by hot foil blocking onto the sheet. The foil may also be formed by sputtering to the desired thickness.

BACKGROUND OF THE INVENTION

This invention relates to antennas. In one form it relates to an antennawhich is particularly suitable for, but not limited to, receivingtelevision signals. The invention is also applicable to antennas forradio transmission and reception.

Conventional television antennas are generally quite bulky andunsightly. In order to achieve best performance, outdoor antennas arepreferred, for example, roof mounted antennas. However, these can beinconvenient to mount securely, and difficult to maintain. In the eventof a storm, an outdoor antenna may easily become mis-aligned, or it maysuffer damage.

Indoor antennas are commonly smaller than outdoor antennas for aestheticreasons. However, their small size limits their efficiency, which meansthat they are generally suitable for reception only in areas where thetelevision signals are strong. A tuned Yagi antenna has additionalelements to increase gain, but this achieves high gain only along thefront-rear direction of the antenna. Thus the antenna is highlydirectional and is also susceptible to receiving rear-reflected signalsto cause ghosting. Typically the acceptance angle of a Yagi antenna isonly about 20 degrees.

A lightweight FM-VHF-UHF antenna consisting of strip conductors disposedon a flexible plastics sheet has been proposed, see GB-A-1 302 644. Theantenna is in 3 sections, one having the strip conductors disposed in alog periodic array, with the other two sections having the stripconductors disposed each in a Yagi-Uda array.

The present invention is concerned with providing a generally planarantenna of improved design, of compact size yet with sufficient gain fordomestic television reception.

SUMMARY OF THE INVENTION

According to the present invention there is provided a generally planarantenna as specified in the claims hereinafter.

The antenna of the invention comprises at least one, and preferably atleast two pairs of spaced-apart electrically-conducting lands acting asdipoles disposed on an electrically-insulating sheet material.

The antenna is designed to be deployed vertically broadside on to atransmitter generating horizontally-polarized signals. The antenna canbe employed on its side, horizontally, for vertically-polarized signals.

The sheet material may be flexible (e.g. of plastics material) or it maybe relatively rigid—for example a stiff cardboard sheet.

The electrically-conductive lands may be formed by a variety of means(e.g. printing, laminating, etching, evaporation), but preferably theyare formed of foil (e.g. aluminium foil) hot pressed onto the sheetmaterial.

An antenna feed arrangement is associated with one pair of lands, otherpairs of lands (if present) act as a reflector. Three pairs of lands maybe employed side-by-side with the feed being taken from any pair, forexample the centre pair. With a vertically disposed antenna the feed ispreferably taken from the bottom of the antenna.

Each pair of lands is preferably spaced-apart from and symmetrical aboutan imaginary line on the sheet material. The first pair of lands mayform a first symmetric shape with each further pair forming the same ordifferent symmetric shapes.

Each land is a substantially two-dimensional area with an x-axisparallel to the imaginary line and a y-axis orthogonal thereto, with themaximum x-dimension of each land being approximately the same or similarto the maximum y-dimension. In other words each land extendssubstantially in both x- and y-directions—in contrast to a thin strip.

Each land may be generally rectangular or trapezoidal. The shape anddimensions of the lands, and their spacing, will vary the output of theantenna.

The lands do not need to be disposed on the same side of the sheetmaterial although this is preferred.

A land of one pair may be capacitively coupled to a land of another pair(e.g. diagonally if two pairs of lands are side-by-side). This may beachieved by having these lands on opposite sides of the sheet materialand extending the foil in a thin strip from one such land towards asimilar strip from the other land (on the opposite side of the sheet)until the strips overlap capacitively. The sheet material acts as thecapacitive dielectric.

In order to improve performance, means may be provided, such as a clip,for shorting together any pair of the lands not coupled to the antennafeed means. In certain circumstances this has proven to increasetelevision band selectivity. The shorting may be controlled by a switchor by simply removing the clip.

If desired, to improve performance two or more antennas of the inventioncan be coupled together and stacked in series.

If the antenna is compact enough, it will be possible to integrate itwith a domestic television receiver—for example in or on the back of thereceiver or even (if the conductive lands are sufficiently thin andoptically transmissive) on the viewing face of the cathode ray tube.

DETAILED DESCRIPTION OF THE INVENTION

A preferred antenna according to the invention, for use with a domestictelevision receiver, will now be described by way of example withreference to the accompanying drawing. The drawing shows the antennaface-on.

The antenna comprises a sheet 1 of stiff cardboard to which has beenlaminated by hot foil blocking four spaced aluminium foil lands 3,5,7and 9. The aluminium foil is approximately 200×10⁻¹⁰ metres inthickness, which gives an electrical resistance of about 1.5 ohms persquare. The foil is overcoated with an electrically-insulating lacquer.

The arrangement may be manufactured by sputtering aluminium to thedesired thickness onto a lacquer-coated backing surface. The aluminiumis then coated with adhesive and the combination hot foil blocked ontothe sheet 1 with the adhesive adjacent the sheet. The backing surface ispeeled away to leave the sheet 1, lands 3, 5, 7, 9 and lacquerovercoating bonded together.

Each pair of lands 3,5 and 7,9 is spaced apart from and is symmetricalabout an imaginary line x-x on sheet 1.

The antenna is designed for use in a vertical plane, e.g. mountedagainst a wall, and the feed for television signals can be obtained fromeither pair of lands. With the lands shaped as shown, taking feeds fromlands 3,5 is effective for television bands A,B whereas feeds from lands7,9 is more efficient for bands C,D.

The feed (shown to lands 3,5) consists of a clip 11 which presses a pairof strip conductors 13,15 down onto the lacquer at adjacent corners ofthe lands 3,5. The contact to the aluminium foil is capacitive throughthe intervening lacquer (it can also be a direct metal-to-metal contact,without intervening lacquer) Shorting the non fed pair of lands (7,9 asshown) can improve band selectivity, and this can be achieved byshorting across a small area 17 of exposed foil on each land.

The lands are spaced-apart in the y-direction (orthogonal to x-x) by 1cm.

Lands 3,5 each have a maximum y-dimension of 22 cm and a maximumx-dimension of 12 cm. Lands 7,9 have a maximum y-dimension of 22 cm anda maximum x-dimension of 18 cm. At their closest approach lands 3,5 arespaced from lands 7,9 by 15 cm in the x-direction (parallel to x-x).

In a further embodiment which is a variant of that illustrated, the twolands 7 and 9 are merged to form one contiguous land extendingtransverse to x-x and symmetrically relative thereto, to act as a singlereflector to lands 3 and 5.

What is claimed is:
 1. A sheet antenna comprising: a sheet ofelectrically-insulting material; antenna feed means comprising anelectric source, a first feed element connected to said electric source,and second feed element connected to said electric source; a first pairof electrically conducting lands comprising a first land and a secondland, said first land and said second land being disposed on said sheet,wherein said first land is electrically connected to said first feedelement and said second land is electrically connected to said secondfeed element and said first land and said second land are positionedsymmetric about and spaced apart from an imaginary line on said sheet;and a second pair of electrically conducting lands, comprising a thirdland and a fourth land, said third land and said fourth land beingdisposed on said sheet, wherein said second pair of lands isspaced-apart from said first pair of lands along the imaginary line,electrically-insulated from said first pair of lands, and wherein saidthird land and said fourth land are symmetric about the imaginary linewherein each land in said first and said second pair of lands issubstantially two-dimensional with an x-axis parallel to the imaginaryline and a y-axis orthogonal thereto, the maximum x-axis dimension beingabout the same as the maximum y-axis dimension for each said land.
 2. Anantenna as recited in claim 1, wherein each land is substantiallytrapezoidal in shape.
 3. An antenna as recited in claim 1 furthercomprising a third pair of electrically conducting lands positionedsymmetric about, and spaced apart from the imaginary line on said sheet,wherein one of said first, said second or said third pair of lands ispositioned substantially between the remaining two pairs and isconnected to said antenna feed means.
 4. An antenna as recited in claim1 wherein each land in said first and said second pair of landscomprises a conductive foil attached to said sheet ofelectrically-insulating material and having an electrically-insulatingcoating there over.
 5. An antenna as recited in claim 1 wherein saidantenna feed means capacitively couples to the lands of said first pairof electrically-conducting lands.
 6. An antenna as recited in claim 5wherein said antenna feed means comprises a clip having feed elementsfor attachment to said sheet material and for urging said feed elementsinto a capacitive coupling arrangement with the lands of said first pairof electrically-conducting lands.
 7. An antenna as recited in claim 1wherein said antenna is disposed vertically within or on a televisionreceiver.
 8. An antenna as recited in claim 1 wherein said antenna iswall-mounted.
 9. A sheet antenna comprising: a sheet ofelectrically-insulting material; a first pair of electrically-conductinglands disposed on said sheet, positioned symmetric about and spacedapart from an imaginary line on said sheet; antenna feed meanscomprising a first feed element and second feed element for formingrespective feed connections to each land in said first pair ofelectrically-conducting lands; and a second pair of electricallyconducting lands disposed on said sheet and spaced-apart from said firstpair of lands along the imaginary line, electrically-insulated from saidfirst pair of lands, and symmetric about the imaginary line, whereineach land in said first and said second pair of lands is substantiallytwo-dimensional with an x-axis parallel to the imaginary line and ay-axis orthogonal thereto, the maximum x-axis dimension being about thesame as the maximum y-axis dimension for each said land.